It has been known that methylation of genomic DNA in a living organism is caused to suppress expression of mRNA. Further, it has been reported that the difference of methylation pattern on a genome relates to genesis, differentiation, and disease such as cancer, and therefore the analysis of methylation of genomic DNA has an important role in finding out the cause and prevention of disease, development of medicinal products, research on the regenerative medicine, and so on.
On the other hand, as the method for determining methylated cytosine in DNA nucleotide sequence, a method for comparing the fragments by methylation-sensitive restriction enzyme, a bisulfite method, a methylation-specific PCR method, and a method which utilizes a high performance liquid chromatography (HPLC), etc have been known. Among them, the bisulfite method has become popular as a common method because the bisulfite method is low cost and applicable to high throughput, and is also effective for sequencing and screening.